Known in the prior art are hydraulic drives comprising a gas-hydraulic accumulator communicating via a distributing device with the User, e.g. the space of the hydraulic power cylinder of a press. To make up for the used-up fluid such a hydraulic drive is provided with a pump intended to transfer fluid from a reservoir into the accumulator.
A disadvantage of the prior-art hydraulic drive consists in the necessity of checking the fluid level in the accumulator.
The absence of means for controlling the fluid level in the accumulator results in variations in said level and, as a consequence, in variations of the initial pressure in the hydraulic cylinder. A considerable rise of this level may bring about an emergency build-up of pressure whereas dropping of the level may permit gas to penetrate into the User's hydraulic system, e.g. hydraulic cylinder of the press, which will endanger the servicing personnel.